GOULDIAN GENETICS

INTRO

Genetics can be a topic of confusion and frustration especially when dealing with a species such as the Gouldian finch. To date there have been numerous color mutations developed. This page is written to break down some key principles of their genetics, and do it in a way that even a person who does not have a deep understanding of genetics can understand.

HISTORY AND ECOLOGY OF THE GOULDIAN FINCH:

Gouldian finches occur in two primary head colors in the wild, red, and black. There is a third color orange that most likely would not survive long in the wild and represents a very low fitness level. The red headed and black headed Gouldian are thought to have occurred in Australian in separate geographical regions and therefore there was a fitness advantage associated with the different head colors. Separation by large geographical regions for long periods of time can bring about speciation or subspecies.

DISTINCTIVE POPULATIONS?

A common way to decide if an organisms belongs to a different subspecies of the same species are if they are capable of interbreeding and producing fertile offspring. They normally do not interbreed in nature due to geographic isolation, sexual selection, or other factors.

The differences between subspecies are usually less distinct than the differences between species. In the case related to difference of head coloration and offspring mortality in Gouldians this can be seen. Research done by [Pryke and Griffith, 2009] went on to show that black headed birds outnumber red headed bird in the wild 3:1. How could this be when we know that the red head gene is dominate to black head?
Their research further emphasized that even though red headed birds could produce fertile offspring with black headed birds; their resulting offspring had a lower level of fitness and higher mortality levels than birds mated to the same head color. At some point the geographical barrier was removed, and the two or more distinct populations were allowed to converge and interbreed.
I theorize that the tropical savannah woodlands that the Gouldian’s rely on at one time was divided. Later events occurred such as fires that allowed the movement of suitable habitat to converge back up to present day conditions. Even though birds of opposite head color were capable of producing fertile young there appeared to be subtle differences genetically that influenced higher mortality.

WHY DO BLACK HEADED BIRDS OUTNUMBER RED HEADED BIRDS?

So back to the question why do black headed birds outnumber read headed birds in the wild? There are several hypothesis that consider that the “both male and female red morph birds are very aggressive and thus end up with the best nesting cavities. Because red-headed birds have very high plasma testosterone concentrations, the male spends most of his time fighting instead of helping his mate raise their chicks.
Elevated testosterone levels and high-stress lives compromise the bird’s immune systems, making both males and females shorter-lived than individuals of the other color morphs. These traits are a predisposition to health problems, such as air sac mite infection and due to the higher stress susceptibility they are unable to retain normal immunity level. In the times when numbers of wild-living populations declined dramatically due to capture, most of the females lacking options for choice in an appropriate mating partner, probably mated with different colored males. The higher count on these different pairs might have had a negative effect on the capability of the local populations to grow, due to the reduced porbablility of fledgling survival and higher rate of males among the surviving population.
Black-headed birds, which comprise approximately 70 percent of the wild population, are less aggressive than the red-heads, and have correspondingly lower testosterone levels. Black morphs usually lose the best nesting cavities to red morph birds, but the black morph males share chick rearing duties with their mates, and both sexes live longer.” [Pryke, S., & Griffith, S. 2009]

REPRODUCTIVE FITNESS IN CAPTIVE BIRDS BREED TO OPPOSITE HEAD COLORS

The Gouldian finch was described by British ornithological artist John Gould in 1844. Some years later the birds began flooding the European market. The Gouldian finch were highly prized then as they are today for their extraordinary colors.
Fast forward today nearly 150 years later and you realize that the birds found in captivity are somewhat different that the wild birds. Since its introduction into captivity indiscriminate breeding regardless of head color resulting in the birds of today. They show no decreased fitness when forced to breed with birds of opposite head color.

So contrary to what people say or what Pryke and Griffith discovered breeding birds of opposite head colors from captive breeding stock does not negatively affect survivability of chicks.
Another study did however find that hens have the ability to control the sex of their chicks due to head color of their mate.

PLUMAGE COLOR INFLUENCES CHOICE OF MATES AND SEX OF CHICKS [Pryke, S., & Griffith, S. 2009]

A research article conducted by Pryke, and Griffith showed that when a female is forced to mate with the opposite head color that a significantly higher ratio of male offspring are produced. Conversely if a female is paired up to the same head color she produces nearly even numbers of both sexes. Dr. Pryke even went as far as to disguise males to appear visually as the opposite head color than what they really were. It worked, and tricked the hens to invest more into breeding and they produced larger clutches and even sex ratios.

HEAD COLOR INHERITANCE

“The plumage colors of these birds’ heads is a genetic trait, with red being dominant to yellow, which is partially dominant to black. Further, red and black head colors are a sex-linked trait in Gouldian finches, and because birds have ZZ/Zw chromosomal sex determination, only the males (ZZ) can have two genes for red head color (homozygous), while females (Zw) can only ever have one gene for red head color (hemizygous). In contrast, yellow head color is an autosomal recessive trait, but is only ever fully expressed when the bird carries one copy of the red gene. In the absence of the red gene, birds that are homozygous for the yellow autosomal trait will have black heads and yellow-tipped beaks instead of the typical red-tipped beak.” [Pryke, S., & Griffith, S. 2009]
Red headed birds can produce offspring with either red, yellow or black head plumages and a yellow bird can also produce offspring with either red, yellow or black heads, while black morphs produce only black-headed chicks.